FIG. 1 is a diagram showing an example of a wireless communication system to which the present invention is applicable. FIG. 1 shows two kinds of user equipments (UEs): a primary UE directly connected to a base station (e.g., an eNB) 110 to exchange a signal with a network and a secondary UE for exchanging a signal with a network via the primary UE. FIG. 1 shows a primary UE1 120 and a primary UE2 130 as an example of a primary UE and a secondary UE1 140 and a secondary UE2 150 as an example of a secondary UE. The secondary UE1 140 and the secondary UE2 150 may communicate with the primary UE1 120. The primary UE and the secondary UE may be referred to as a master UE and a slave UE, respectively. For example, the primary UE1 120 may serve to relay a signal transmitted by the secondary UE1 140 and/or a signal transmitted to the secondary UE1 140 between the secondary UE1 140 and the eNB 110. If one UE serves as a relay for another UE, a UE-relay scheme may be applied. FIG. 1 shows operation for exchanging a signal between the primary UE1 120 and the secondary UE 140 and/or 150 within coverage of the eNB 110.
One or more secondary UEs may be connected to one primary UE and the primary UE may serve to control transmission/reception operations of a plurality of secondary UEs connected thereto. The primary UE may be, for example, a general mobile telephone and the secondary UE may be a low-power communication device attached to a laptop computer, a music player or a bio signal sensor. For example, the primary UE and the secondary UE may be possessed by the same user.